The alveolar aerial gradient is highest in which of the following?

The alveolar aerial PO2 difference is obtained by subtracting the aerial PO2 from the alveolar PO2. The normal alveolar-arial PO2 gradient is between 5-15 mm Hg.The alveolar aerial gradient is useful measure of ventilation perfusion mismatch. ILD- Due to pulmonary fibrosis, diffusion defect will lead to significant reduction in value of paO2. Hence the gradient will show an increase. Pulmonary embolism- Due to V/P mismatch in PE, the value of paO2 is normal to reduced. In massive PE, the gradient is definitely increased. There is adequat ventilation but zero perfusion , the V/Q ratio is infinite.At a ratio of infinity, there is no exchange of gases through the respiratory membrane of affected alveoli. Acute severe asthma- Due to severe airflow limitation both paO2 and pAO2 are reduced leading to normal alveolar aerial gradient. FB leading to upper airway obstruction- Due to severe airflow limitation both paO2 and pAO2 are reduced leading t normal alveolar aerial gradient.